Fashion writer Isioma Daniel is reported to have left Nigeria after calls for her to be killed for insulting the Prophet Mohammed.

Colleagues at ThisDay newspaper say she is now in the United States, according to Reuters news agency.

ThisDay newspaper has apologised on her behalf, so the fatwa has to be withdrawn

Ali AlkaliIslamic scholar

On Tuesday, authorities in the northern state of Zamfara issued what they said was a "fatwa", urging Muslims to kill her for writing the article, which sparked religious riots in the northern city of Kaduna.

At least 220 people were killed in several days of clashes between the city's Muslims and Christians. Kaduna is now reported to be calm.

A fatwa is a religious decree which is normally made by an Islamic scholar but a spokesman for Zamfara state said that any leader could issue one.

Opinion is divided among Muslim leaders about whether the Zamfara fatwa is indeed valid.

Some say that because Ms Daniel has apologised and also resigned from her job, she does not deserve to be killed.

Political divide

The new journalism graduate wrote an article in response to Muslim objections to Nigeria's hosting of the Miss World beauty contest, saying that the Prophet Mohammed would not have complained about the pageant and indeed, may have chosen to marry one of the beauty queens.

This infuriated many Muslims, who destroyed ThisDay's Kaduna office and went on to burn down churches and hotels last week.

Correspondents say this is the latest example of a split between politicians in the Muslim north and the federal government, which is largely made up of southern Christians.

President Olusegun Obasanjo, a born-again Christian, is seeking re-election next year.

The federal government has said that it will not allow the death sentence to be carried but no action is being taken against the deputy governor of Zamfara state.

"It is binding on all Muslims wherever they are, to consider the killing of the writer as a religious duty".

The Miss World contest was moved to London after the riots.

A Muslim cleric in the capital, Abuja, said that Ms Daniel could only escape the death penalty by converting to Islam.

Hussein Muhammed told the BBC Focus on Africa programme that if he saw her, he would kill her, even if that meant going to prison because Islamic law is more important to him than Nigerian law.

"I would be willing to kill my parents for Mohammed," he said.

But other Muslim leaders have a different view.

"ThisDay newspaper has apologised on her (Ms Daniel's) behalf, so the fatwa has to be withdrawn," Kaduna-based Islamic scholar Ali Alkali told Reuters.

Ann Cooper, executive director of the New York-based Committee to Protect Journalists said: "We are extremely concerned about her safety. In this whole controversy, I think something that has been completely lost is the universal right to free expression."